linux-kernel - Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack

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Date:	Thu, 14 Jul 2016 09:01:27 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	Oren Laadan <orenl@...lrox.com>,
	Ruchi Kandoi <kandoiruchi@...gle.com>,
	Rom Lemarchand <romlem@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>,
	Todd Kjos <tkjos@...gle.com>, Colin Cross <ccross@...roid.com>,
	Nick Kralevich <nnk@...gle.com>,
	Dmitry Shmidt <dimitrysh@...gle.com>,
	Elliott Hughes <enh@...gle.com>
Subject: Re: [PATCH 2/2] proc: Add /proc/<pid>/timerslack_ns interface

On Thu, Jul 14, 2016 at 6:42 AM, Arjan van de Ven <arjan@...ux.intel.com> wrote:
> On 7/14/2016 5:48 AM, Serge E. Hallyn wrote:
>
>> Can someone give a detailed explanation of what you could do with
>> the new timerslack feature and compare it to what you can do with
>> sys_nice?
>>
>
> what you can do with the timerslack feature is add upto 4 seconds of extra
> time/delay on top of each select()/poll()/nanosleep()/... (basically
> anything that
> uses hrtimers on behalf of the user), and then also control within that
> 4 second window exactly when that extra delay ends
> (which may help a timing attack kind of scenario)

So the interface actually allows for 64bits of nanoseconds, so more or
less infinite delay if nothing else is happening.

thanks
-john